Esme Povirk (@madewokherd) commented about dlls/comdlg32/itemdlg.c:
MapWindowPoints(NULL, This->dlg_hwnd, (POINT*)&toolbar_rc, 2);
INT w, h;
GetWindowRect(hwnd, &navbar_rc);
navbar_rc.left = dialog_rc.left;
navbar_rc.right = dialog_rc.right;
MapWindowPoints(NULL, This->dlg_hwnd, (POINT*)&navbar_rc, 2);
w = navbar_rc.right - navbar_rc.left;
h = navbar_rc.bottom - navbar_rc.top;
navbar_rc.top = hspacing;
navbar_rc.bottom = navbar_rc.top + h;
navbar_rc.left = hspacing;
navbar_rc.right = w - hspacing;
I don't think the result of GetWindowRect and MapWindowPoints is actually used here, other than the height? And since the height is fixed at 30 DIPs, we probably don't need it for that either.